ch 18 - prokaryotic gene regulation Flashcards
what contributes to the genetic diversity of bacteria (prokaryotes)
rapid reproduction, mutation, and genetic recombination
bacterial chromosome
a circular DNA molecule with few associated proteins
plasmids
smaller circular DNA molecules that can replicate independently of the bacterial chromosome
contains small number of genes not required for survival
contains genes that give bacteria an advantage
replicate separately from other dna
how do bacterial cells divide
by binary fission
preceded by replication of the bacterial chromosome
recombination in bacteria
three processes bring bacterial DNA from different individuals together
conjugation
transduction
transformation
bacteria try to pass on genome
recombination - conjugation
bacteria and bacteria
8recombination - transduction
bacteria and virus
recombination - transformation
bacteria and nothing
naked dna
bacteria response to environment
bacteria can cope with environmental fluctuations by exerting metabolic control
cells can turn on or off soecific genes or adjust the activity of enzymes already present
operons
basic mechanism for gene expression
genes often clustered into operons
operons can be turned on or off by different proteins that interact directly with the DNA near the region of the gene
operon parts
regulatory/repressor gene codes for the repressor protein
promotor site - attachment site for RNA polymerase
operator site - attachment site for repressor protein
structural genes - codes for the proteins of interest
repressible operons
the gene that is coded for is usually on
binding of a specific repressor protein to the operator shuts off transcription
repress expression with attachment
inducible operon
usually off
binding of an inducer to an active repressor protein inactivates the repressor and turns ON transcription
repressible operon - trp operon
trp operon normally on
RNA polymerase can bind to promoter and transcribe the genes of that operon
trp operon usually on and codes for proteins that synthesize tryptophan
repressed by pressence of tryptophan
how does tryptophan repress trp
regulatory gene mRNA makes trp repressor protein but protein is inactive
typically RNA polymerase moves along operator and genes of operon
when tryptophan is present it can bind to protein at nonactive site
protein is activated and binds to operator on DNA
RNA polymerase can therefore no longer move passed promoter
more tryptophan = more operators turned off = less tryptophan made
lac operon
lactose available/present to E.coli if host drinks milk
lactose broken down to monosaccharides by enzyme beta - galactosidase
beta - galactosidase not always made by E. coli
only made when necessary
lactose absent
repressor is active and operon is odd
the lac repressor is innately active and RNA polymerase is off bc no need to make enzymes to digest lactose since no lactose is present
lastose present
when lactose is present it binds to regulatory protein which inactivates it
then the RNA polymerase can move passed promoter and enzymes that break down lactose are formed
importance of lac operon
many bacterial genes are under negative control by repressor proteins
introduced a fundamentally important idea : gene expression is reguated by physical contact between regulatory proteins and specific regulatory sites in DNA
when we need to transcribe beta-galactosidase, two molecules are necessarary
cyclic AMP (CAMP)
binds to CAP+
and RNA polymerase
CAMP + CAP complex binds near polymerase and helps get polymerase in the right place
lactose and glucose levels relationship
lactose is only used as an energy source when a better carbohydrate source isn’t present
when glucose is present, CAMP levels are low, so they can’t bind to CAP and initiate enzyme production = no transcription
